| In the auto cruise example, it’s leaving perhaps 2 - 2.5 car distances. In close traffic the average human I would bet is leaving 1 or less then 1. The issue is not that I can’t rebuild the following distance, the point I’m trying to make is that even if I constantly rebuild the following distance it sets off a cascading effect. I’m following at set speed, car cuts in front, hits brakes, I now slow down, car behind me slows down, I rebuild following distance and car perhaps 7-8-9 cars behind me repeats because at some point the cascade magnifies to a larger slowdown behind. Can I mitigate this by manually letting my distance be closer for a time, and slowly easing to larger ? Yes. But if I allow the car to do it automatically, it will increase the follow distance at a rate that causes a cascade in tight traffic. Though - I do think with these discussions on HN- it does depend on where you’re driving. My experiences are centered on East Coast, thinking of route 80, 81, 83, etc. or Philly / New York City. The driving experience is radically different in California, Florida , or the mid west. I would say when driving in California people seem to navigate traffic better. (SF, LA) then on drivers on 80/81/83.
(Or perhaps it’s due to better designed roads ). |
At 60 kph (16.7 m/s) 1 car distance (about 5 m) is less than one third of a second. Even 2.5 car lengths is less than a second. I use traffic aware cruise control on my Tesla set to the maximum separation which is about three seconds, so 50 m at 60 kph.
Three seconds separation is in fact the recommended following separation in most European countries and in Germany in particular 0.9 seconds or less can result in a hefty fine, see https://en.wikipedia.org/wiki/Two-second_rule
In the UK some stretches of motorway have chevrons marked on the road indicating the required spacing at the speed limit.